The Hsp40 co-chaperone DNAJC7 modifies polyglutamine but not polyglycine aggregation.

Polyglutamine (polyQ) diseases, including Huntington's disease and several spinocerebellar ataxias, are caused by abnormally expanded CAG nucleotide repeats, which encode aggregation-prone polyQ tracts. Substantial prior evidence supports a pathogenic role for polyQ protein misfolding and aggregation, with molecular chaperones showing promise in suppressing disease phenotypes in cellular and animal models. In this study, we developed a FRET-based reporter system that models polyQ aggregation in human cells and used it to perform a high-throughput CRISPR interference screen targeting all known molecular chaperones. This screen identified as a strong suppressor of polyQ aggregation the Hsp40 co-chaperone DNAJC7, which has previously been shown to modify aggregation of other disease proteins (tau and TDP-43) and has mutations causative for amyotrophic lateral sclerosis. We validated this phenotype and further established a physical interaction between DNAJC7 and polyQ-expanded protein. In contrast, DNAJC7 did not modify aggregation of polyglycine (polyG) in a FRET-based model of neuronal intranuclear inclusion disease. In addition to establishing new inducible, scalable cellular models for polyQ and polyG aggregation, this work expands the role of DNAJC7 in regulating folding of disease-associated proteins.